1. Field of the Invention
The present invention relates in general to power distribution for electronic devices, and more particularly, but not exclusively, to automatic transfer switches for use in computing environments.
2. Description of the Related Art
An automatic transfer switch (ATS) is a circuit that automatically connects one of two alternating current (AC) line sources to an electrical load. Transfer switches may be seen where emergency power generators are used to provide back up power from the utility source. The transfer switch allows switching from utility power to emergency generator power during main line outages. An automatic transfer switch must totally isolate the two input sources.
In order to switch over from one input source to another, an ATS must either actively monitor the conditions of the two input lines and makes a disconnect and connect decision, or be designed such that it reactively connects the correct input source based on its circuitry's relative response to the changing states of the competing input sources.
The first, active monitoring option generally uses microcontrollers for the purpose of monitoring and control. Such active monitoring ATS devices generally use microcontroller-based “smart” electronic control circuits to drive low voltage coils for the purpose of opening and closing power contacts. The active monitoring and control approach provides repeatable operation at any line voltage. Supporting the microcontroller, however, requires house keeping power supplies, voltage sensors, signal condition circuitries, and control firmware. These additional requirements add to the system cost and complexity. The added complexity, in turn, degrades reliability.
The second, reflexive option is often a simple design based on interlocking mechanical contactors that open or close based on the voltage applied to their driving coils. This second option is much simpler and less expensive to implement but suffers from a major weakness as described below.
Different regions in the world have different power characteristics, more specifically the AC input voltages vary from country to country. As in most electrical designs, the ATS devices should not be region-specific; otherwise separate part numbers must be specified on a per-region, or worse, on a per-country basis. In the case of the reflexive design, even though a number of contactors of differing part numbers can be used to cover the worldwide power requirements, these part numbers do not correspond to line cord options for larger areas, such as Europe and/or the United States. In other words, there is not a single part number for a contactor that can fully cover Europe as is the case with line cord options.